Refractor

A refractor is a telescope that focuses light using a glass lens, called the objective, mounted at the front of a sealed tube. Light bends as it passes through the curved glass and comes to a focus near the back of the tube, where an eyepiece or diagonal sits. Because the tube is sealed, dust rarely reaches the internal optics, and the lens almost never needs the kind of realignment a mirror-based telescope does.

Refractors are popular for their sharp, high-contrast views, especially on the Moon and planets, and their simplicity makes them a common recommendation for beginners who want a telescope that works reliably right out of the box. The tradeoff is cost: a large-aperture refractor is significantly more expensive to manufacture than a mirror of the same size, since large lenses of optical quality are harder to produce than large mirrors.

Cheaper refractors can show color fringing around bright objects, caused by different wavelengths of light focusing at slightly different points, an effect that better-corrected and apochromatic designs reduce. When buying, check whether a refractor is described as achromatic or apochromatic, since that single detail affects both price and how clean the view will look around bright stars and planets.